The present invention relates to a control valve for a variable displacement compressor. More specifically, it relates to an independently controllable and compact control valve for varying the amount of discharged refrigerant gas based on internal pressure acting on a displacement control mechanism and an external signal.
A cooling circuit or a refrigerant circulation circuit is provided with a compressor for compressing refrigerant gas. Usually, when a passenger turns on an air conditioner in a vehicle, drive power is transmitted from an engine to the compressor. Automotive compressors of conventional technology are generally categorized into two types. One is with a compressibility controller which autonomously controls compression capability or an amount of refrigerant gas to be discharged corresponding to a cooling load. The other is with an electromagnetic clutch which externally controls the linkage between the compressor and the engine.
Generally, the compressibility controller has a displacement control mechanism for varying the amount of discharged refrigerant gas based on the controlling pressure and an internal control valve mechanism for controlling the controlling pressure. The controlling pressure corresponds to pressure as a cooling load such as suction pressure, that is the pressure at which refrigerant gas is drawn into the compressor. One of the displacement control mechanisms of a piston type compressor, for example, changes the inclination angle of a cam plate which converts rotational movement by an engine into reciprocating movement of a piston. The change in inclination angle of the cam plate varies the stroke distance of the piston, thereby varying the amount of discharged refrigerant gas from the compressor. One of the internal control valve mechanisms includes the pressure reacting member for sensing the fluctuation of pressure in the cooling load and a valve body for changing the opening degree of a refrigerant passage in response to the pressure reacting member so as to change the controlling pressure. In other words, movement of the pressure reacting member varies the position of the valve body to cause a change in the opening degree of the refrigerant passage ultimately in the controlling pressure.
When a cooling load demands, the compressor is connected to the vehicle engine through an electromagnetic clutch to start the compression process. During the compression, the amount of discharged refrigerant gas is controlled based on the cooling load such as suction pressure. If a passenger turns OFF the air conditioner in a vehicle, which is considered to be an external xe2x80x9cOFFxe2x80x9d command, the electromagnetic clutch shuts down the power transfer from the engine to the compressor, thereby shutting down the compression operation.
Nonetheless, the electromagnetic clutch in a compressor has increased the total weight of the system, manufacturing cost, and mechanical shock generated when the electromagnetic clutch is turned on. The market demanded a solution of the drawbacks and a new compressor without a clutch or a clutchless compressor which is directly connected to the compressor and the engine for vehicles so as to transmit power all the time.
To fulfill the demand for a clutchless compressor, the amount of discharged refrigerant gas is variably made to nearly nothing in response to an external command without an electromagnetic clutch. However, the ability of the internal control valve mechanism is limited to an autonomous control of the amount of discharged refrigerant gas based on a cooling load, but not on an external command.
Japanese Unexamined Patent Publication No. 2000-087848 discloses a solution by using a control valve for controlling the amount of discharged refrigerant gas from a compressor. This control valve has a valve body capable of varying an opening degree of refrigerant passage for changing the controlling pressure, a pressure reacting member capable of reacting to the cooling load, and an electromagnetic actuator capable of applying external force to the valve body. The valve body is linked to the pressure reacting member and a plunger being actuated by the electromagnetic actuator. The electromagnetic actuator is capable of applying external force to the valve body upon receipt of an external command so as to vary the opening degree of the refrigerant passage. As a result, the amount discharged of refrigerant gas is externally and independently controlled by varying the opening degree of the refrigerant passage.
On the other hand, a control valve disclosed in Japanese Unexamined Patent Publication No. 7-189899 has an internal control valve and an external control valve. The internal control valve has a valve body capable of varying an opening degree of refrigerant passage for changing the controlling pressure and a pressure reacting member capable of reacting to the cooling load, which is linked to the valve body. The external control valve has a valve body capable of varying an opening degree of refrigerant passage for changing the controlling pressure and an electromagnetic actuator capable of applying force to the valve body. The electromagnetic actuator is capable of applying force to the valve body upon receipt of an external command so as to vary the opening degree of the refrigerant passage. As a result, in this publication also the amount of discharged refrigerant gas is externally and independently controlled by varying the opening degree of the refrigerant passage. The internal control valve mechanism and the external valve control mechanism are also disposed in two separate control valve housings, and the control valve housings take a substantial portion of the rear housing space.
However, in the control valve as disclosed in Japanese Unexamined Patent Publication No. 2000-087848, a pressure reacting member and a plunger are linked to the valve body so as to move in response to the valve body. The control valve requires an apparatus varying the amount of power supply to the electromagnetic actuator for actuating the plunger and makes the construction of the control valve complex. If one tries to actuate the electromagnetic actuator without the variable power supply control apparatus, the electromagnetic actuator must be turned ON/OFF by stopping and starting the flow of electric current. This method has the following drawback. Normally, when the electromagnetic actuator is turned on by a switch, the voltage supplied to the electromagnetic actuator depends on the voltage of a battery installed in the vehicle as a power source. In other words, the external force that the electromagnetic actuator applies to the valve body is affected if a charge level of the battery supply has fluctuated. As a result, the opening degree of the refrigerant passage is affected by the fluctuation of the external force, making it difficult to control the controlling pressure depending on an opening degree of the refrigerant passage.
Furthermore, the control valve disclosed in Japanese Unexamined Patent Publication No. 7-189899, needs to manufacture two control valve housings. This increases not only assembling process, but also a space occupied by the control valve.
The object of the present invention is to offer a control valve for a variable displacement compressor and a variable displacement compressor capable of varying the amount of discharged refrigerant gas based on an autonomous change of the amount of discharged refrigerant gas from the compressor corresponding to the cooling load and based on an external command, of which construction is simplified to be compact.
To achieve the above object, the present invention has following features. A control valve is used in connection with a variable displacement compressor that varies the discharge capacity by controlling an inclination of a cam plate located in a crank chamber. The inclination of the cam plate is variable based on control pressure in a control pressure region. Monitor pressure is monitored at a predetermined point in a refrigerant circuit for causing a change in the control pressure and ultimately varying the discharge capacity. The control valve has a housing, an internal control valve mechanism and an external control valve mechanism. The internal control valve mechanism is located inside the housing and has a first valve body and a first reacting member. The first reacting member is operably connected to the first valve body for reacting to the monitor pressure to cause a change in the control pressure. The external control valve mechanism is located inside the housing and has a second valve body and a second reacting member. The second reacting member is for reacting to an external signal to cause the second valve body to change the control pressure. The internal control valve mechanism and the external control valve mechanism operate independently.